You really should give it a go I would love to see what you can do with your 150-600 on the D7100 you have more megapixels to play with so should be able to get great detail.
Its amazing how much difference a really clear crisp night vs a night with high thin cloud or haze makes to the detail you can get.
Happened to walking in to work and carrying my camera with the Tamron 150-600 mounted. Someone mentioned how clear the moon was, so I snapped a couple of test shots at varying focal lengths. In the partial light of the setting sun, the autofocus locked right on to the moon. This one was pretty sharp.